Re: ''Update functions'' in Scheme.

One ought not to say things like:
"F(G(C)) := D ought to ensure that F(G(C)) = D afterwards."
too blithely. Consider the array assignment:
A[A[1]] := 2
in a two element array A, where initially A[1]=A[2]=1 . This sort of thing had
program verifiers confused for a good while in the early 70's.
Mitchell Wand
College of Computer Science
Northeastern University
360 Huntington Avenue #161CN
Boston, MA 02115
CSNet: wand@corwin.ccs.northeastern.edu